After 2147483647 milliseconds (~ 25 days) all timers will expire immediately

[0xCAFEDECAF]

https://github.com/aron-bordin/PNG-Arduino-Framework/blob/6f6809e97a4831675feb3f99b39b281648a64d4f/Timer/Timer.cpp#L87

So... after 0x7FFFFFFF (2147483647) milliseconds (~ 25 days), all timers will expire immediately??

From that moment until millis() actually rolls over (at ~ 49 days), LastTime will be set to 0 so that the expression in the next line is always 'true'.

BTW, lines 87/88 are unnecessary because the arithmetic in line 89 has safe roll-over behaviour.